Introducere

The syntax for patterns used in these functions closely resembles
Perl. The expression must be enclosed in the delimiters, a
forward slash (/), for example. Delimiters can be any
non-alphanumeric, non-whitespace ASCII character except the backslash (\) and the
null byte. If the delimiter character has to be used in the
expression itself, it needs to be escaped by backslash. Since PHP
4.0.4, you can also use Perl-style (), {}, [], and <>
matching delimiters.
See Pattern Syntax
for detailed explanation.

The ending delimiter may be followed by various modifiers that
affect the matching.
See Pattern
Modifiers.

The PCRE library is a set of functions that implement regular
expression pattern matching using the same syntax and semantics
as Perl 5, with just a few differences (see below). The current
implementation corresponds to Perl 5.005.